The use of corona discharges in air to provide treatments to modify the surface of various polymer articles to improve their wettability, adhesion properties, ink receptivity, etc. is well known in the art. Such corona treatment apparatus has been used for example in U.S. Pat. No. 3,755,683 (Kiikka and Hartman) to improve adhesive qualities for use in, among other things, heat sealing operations and photographic coating and subcoating operations in which a photographic emulsion, nucleating layer, actinic radiation-sensitive layer, or the like is coated onto the polymeric film.
U.S. Pat. No. 3,761,299 (Lidel) discloses a reduced pressure plasma process for improving the adhesion of vinyl-sulfone-hardened photographic emulsions directly coated on poly(ethylene terephthalate), (PET). The process uses a reactive gas/activator gas to produce a radio frequency (RF) plasma and the inventor specifically states that ". . . the process is extremely inefficient if practiced with ambient pressures . . . ."
U.S. Pat. No. 4,072,769 (Lidel) discloses the direct coating of photo emulsion to PET treated in reactive gas/inert-gas carrier coronas at reduced pressure. From the comparative examples it is not obvious that nitrogen alone would improve photographic emulsion adhesion.
J59-56430 (Tamaki and Tatsuda) disclose plasma treatment of PET in the outgas of the film as it is processed and in low pressure atmospheres of Ar, N.sub.2, O.sub.2, and air and show that even small amounts of these gases degrade the wet adhesion of the emulsion to the substrate.
One of the earliest disclosures of nitrogen atmosphere corona treatment of PET and polyolefins was U.S. Pat. No. 3,639,134 (Stegmeir et al.) wherein nitrogen or carbon dioxide or up to 15% air with nitrogen or carbon dioxide was used as the atmosphere surrounding the corona and wherein the polymer treated was heated between room temperature and 25.degree. C. below its melting point, thus giving increased polymer heat sealability.
EP 5,510 Bl (Deguchi et al) describes a process for preparing a PET film having a nitrogen-containing layer, less than 10 nm thick, with an ESCA atomic ratios of N/C greater than 0.01 using a room temperature nitrogen corona with oxygen concentration less than 0.1%.
U.S. Pat. No. 4,717,516 (Isaka and Nagano) show a process for enhancing adhesion to PET that is corona treated in nitrogen having specific ESCA atomic ratios of N/C and O/C. Control of oxygen is discussed with a preferred range less than 0.1%.
U.S. H688 (Sobataka and Wolfe) describes a process for the nitrogen corona treatment of PET at less than 350 ppm, and preferably less than 5 ppm of oxygen, to improve ink adhesion.
U.S. Pat No. 4,689,359 and U.S. Pat. No. 4,695,532 (Ponticello and Otocka) teach the use of polyethyl acrylate (PEA) as a component in a photographic element to assist in adjusting the hydrophilic and hydrophobic properties of the coated layer.
Flame treatments of polymer films are also well known in the art as a surface modification treatment. Many of these processes have been used to increase the adherence of the polymer surfaces. Representative of film treatment processes are U.S. Pat. Nos. 2,632,931; 2,648,097; 2,683,894; 2,704,382; and 2,746,084.
Fluorine treatments of polymer films have also been used in the art to modify the surface properties of the films, including efforts to improve their adherence. Canadian Patent 1,027,326 discloses the rapid fluorination of polyolefin substrates to improve adhesion. U.K. Patent 1,395,949 discloses the fluorination or carboxylation of polyester materials to improve the dyeability of the surfaces.
U.S. Pat. Nos. 4,296,151; 4,717,623 and 4,743,419 describe various fluorine surface treatments of polymeric films, including olefinic resins and polyesters to improve their surface properties. U.S. Pat. No. 4,717,623 specifically discloses the use of the fluorine treated films to increase the adhesion of radiation-curable coating compositions.